diff --git a/.eslintrc.json b/.eslintrc.json
index 40c12b02e..9ebfebe8f 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -106,7 +106,10 @@
     "prefer-const": "error",
     // Disallow modifying variables that are declared using const.
     // https://eslint.org/docs/rules/no-const-assign
-    "no-const-assign": "error"
+    "no-const-assign": "error",
+    // Require let or const instead of var.
+    // https://eslint.org/docs/rules/no-var
+    "no-var": "error"
   },
   "settings": {
     "svelte3/typescript": true
diff --git a/src/polyfills/typedarray-to-buffer.js b/src/polyfills/typedarray-to-buffer.js
index 1ff9cdbf9..42ebefc04 100644
--- a/src/polyfills/typedarray-to-buffer.js
+++ b/src/polyfills/typedarray-to-buffer.js
@@ -7,7 +7,7 @@ import { Buffer } from 'buffer/';
 
 export default function typedarrayToBuffer(arr) {
   if (isTypedArray.strict(arr)) {
-    var buf = Buffer.from(arr.buffer);
+    let buf = Buffer.from(arr.buffer);
     if (arr.byteLength !== arr.buffer.byteLength) {
       buf = buf.slice(arr.byteOffset, arr.byteOffset + arr.byteLength);
     }